The major protein in myelin of the peripheral nervous system is a glycoprotein. Myelin purified from the central nervous system also contains a glycoprotein, but it is quantitatively a minor component of the isolated myelin. This CNS glycoprotein appears to be selectively concentrated in membranes which are transitional between compact myelin and the oligodendroglial surface membrane. We are purifying this glycoprotein which is in the myelin oligodendroglial complex so that its toxicity and immunogenicity can be studied. This glycoprotein undergoes a chemical change in developing rat brain which may involve its carbohydrate moieties. Since glycoproteins are known to be involved in recognition and contact phenomena, we are investigating its role in developing brain as the oligodendroglial surface membrane makes contact with axons and is spiraled and compacted to form mature myelin. Glycoproteins are also known to be cell surface antigens and receptors for viruses. Therefore, we are investigating the possible role of the myelin-associated glycoprotein in the autoimmune or infectious aspects of multiple sclerosis and other demyelinating diseases.